You are able to lock the door or ask for it’s current status. Unlock by voice isn’t supported for Alexa, kind of security issues.
Iˋm able to do it with a smartapp, setting the action there and set the app to be trigger by a routine. That way you can ask Alexa to turn on the routine.
Here is one related topic for a similar app, take a look there and in the forums, if you really want to setup your ST system, I will need to learn this kind of tricks. Good luck!